Bank Loans and Related Allowance for Credit Losses - Credit Quality Indicators of Bank Loan Portfolio (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 40,477	$ 40,578
Gross charge-offs
Total loans	0	4	$ 1
Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	26,632	25,795
Gross charge-offs
Total loans	0	0	0
First Mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
2023	2,694
2022	6,069	6,444
2021	11,630	12,293
2020	3,974	4,270
2019	851	929
pre-2019	935	1,262
Total loans	$ 26,153	$ 25,198
Percent of Loans on Nonaccrual Status
2023	0.01%
2022	0.02%	0.02%
2021	0.01%	0.03%
2020	0.01%	0.09%
2019	0.01%	0.02%
pre-2019	0.36%	0.43%
Total loans	0.03%	0.06%
First Mortgages | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 26,153	$ 25,198
Gross charge-offs
2023	0
2022	0
2021	0
2020	0
2019	0
pre-2019	0
Total loans	0	0	0
First Mortgages | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
2023	2,694
2022	6,069	6,444
2021	11,630	12,293
2020	3,974	4,270
2019	851	929
pre-2019	935	1,262
Total loans	26,153	25,198
First Mortgages | Origination Loan To Value Ratio 70% and Below | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
2023	1,818
2022	4,492	4,771
2021	10,078	10,641
2020	3,306	3,549
2019	687	749
pre-2019	695	940
Total loans	21,076	20,650
First Mortgages | Origination Loan to Value Ratio Greater Than 70% Through 90% | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
2023	876
2022	1,577	1,673
2021	1,552	1,652
2020	668	721
2019	164	180
pre-2019	238	320
Total loans	5,075	4,546
First Mortgages | Origination Loan to Value Ratio Greater Than 90% Through 100% | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
2023	0
2022	0	0
2021	0	0
2020	0	0
2019	0	0
pre-2019	2	2
Total loans	2	2
First Mortgages | Estimated Current LTV 70% and Below
Financing Receivable, Credit Quality Indicator [Line Items]
2023	1,853
2022	4,855	4,574
2021	11,341	11,751
2020	3,960	4,255
2019	850	928
pre-2019	931	1,257
Total loans	23,790	22,765
First Mortgages | Estimated Current LTV Greater Than 70% through 90%
Financing Receivable, Credit Quality Indicator [Line Items]
2023	841
2022	1,185	1,845
2021	289	542
2020	14	15
2019	1	1
pre-2019	4	5
Total loans	2,334	2,408
First Mortgages | Estimated Current LTV Greater Than 90% through 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2023	0
2022	28	25
2021	0	0
2020	0	0
2019	0	0
pre-2019	0	0
Total loans	28	25
First Mortgages | Estimated Current LTV Greater Than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2023	0
2022	1	0
2021	0	0
2020	0	0
2019	0	0
pre-2019	0	0
Total loans	1	0
First Mortgages | Origination FICO Score Below 620 | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
2023	0
2022	2	3
2021	1	1
2020	1	0
2019	0	0
pre-2019	1	1
Total loans	5	5
First Mortgages | Origination FICO Score 620 Through 679 | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
2023	4
2022	27	28
2021	30	31
2020	20	21
2019	2	2
pre-2019	13	15
Total loans	96	97
First Mortgages | Origination FICO Score 680 Through 739 | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
2023	299
2022	782	820
2021	1,160	1,224
2020	395	430
2019	106	116
pre-2019	188	243
Total loans	2,930	2,833
First Mortgages | Origination FICO Score 740 and Above | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
2023	2,391
2022	5,258	5,593
2021	10,439	11,037
2020	3,558	3,819
2019	743	811
pre-2019	733	1,003
Total loans	23,122	22,263
First Mortgages | Updated FICO Score Below 620
Financing Receivable, Credit Quality Indicator [Line Items]
2023	4
2022	15	11
2021	19	12
2020	8	7
2019	2	2
pre-2019	15	13
Total loans	63	45
First Mortgages | Updated FICO Score 620 Through 679
Financing Receivable, Credit Quality Indicator [Line Items]
2023	46
2022	77	87
2021	87	127
2020	38	42
2019	11	10
pre-2019	39	43
Total loans	298	309
First Mortgages | Updated FICO Score 680 Through 739
Financing Receivable, Credit Quality Indicator [Line Items]
2023	265
2022	575	711
2021	984	1,079
2020	316	378
2019	61	89
pre-2019	108	161
Total loans	2,309	2,418
First Mortgages | Updated FICO Score 740 And Above
Financing Receivable, Credit Quality Indicator [Line Items]
2023	2,379
2022	5,402	5,635
2021	10,540	11,075
2020	3,612	3,843
2019	777	828
pre-2019	773	1,045
Total loans	23,483	22,426
HELOCs
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	479	597
Revolving HELOCs amortized cost basis	311	382
HELOCs converted to term loans	$ 168	$ 215
Percent of Loans on Nonaccrual Status
Total loans	0.84%	0.84%
Revolving HELOCs amortized cost basis	0.07%	0.34%
HELOCs converted to term loans	2.40%	1.90%
HELOCs | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 479	$ 597
Gross charge-offs
Total loans	0	0	$ 0
Revolving HELOCs amortized cost basis	0
HELOCs converted to term loans	0
HELOCs | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	479	597
Revolving HELOCs amortized cost basis	311	382
HELOCs converted to term loans	168	215
HELOCs | Origination Loan To Value Ratio 70% and Below | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	396	485
Revolving HELOCs amortized cost basis	279	332
HELOCs converted to term loans	117	153
HELOCs | Origination Loan to Value Ratio Greater Than 70% Through 90% | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	82	111
Revolving HELOCs amortized cost basis	32	50
HELOCs converted to term loans	50	61
HELOCs | Origination Loan to Value Ratio Greater Than 90% Through 100% | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1	1
Revolving HELOCs amortized cost basis	0	0
HELOCs converted to term loans	1	1
HELOCs | Estimated Current LTV 70% and Below
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	475	594
Revolving HELOCs amortized cost basis	308	380
HELOCs converted to term loans	167	214
HELOCs | Estimated Current LTV Greater Than 70% through 90%
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	4	3
Revolving HELOCs amortized cost basis	3	2
HELOCs converted to term loans	1	1
HELOCs | Estimated Current LTV Greater Than 90% through 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Revolving HELOCs amortized cost basis	0	0
HELOCs converted to term loans	0	0
HELOCs | Estimated Current LTV Greater Than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Revolving HELOCs amortized cost basis	0	0
HELOCs converted to term loans	0	0
HELOCs | Origination FICO Score Below 620 | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Revolving HELOCs amortized cost basis	0	0
HELOCs converted to term loans	0	0
HELOCs | Origination FICO Score 620 Through 679 | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1	2
Revolving HELOCs amortized cost basis	0	0
HELOCs converted to term loans	1	2
HELOCs | Origination FICO Score 680 Through 739 | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	88	106
Revolving HELOCs amortized cost basis	50	59
HELOCs converted to term loans	38	47
HELOCs | Origination FICO Score 740 and Above | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	390	489
Revolving HELOCs amortized cost basis	261	323
HELOCs converted to term loans	129	166
HELOCs | Updated FICO Score Below 620
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	7	7
Revolving HELOCs amortized cost basis	2	2
HELOCs converted to term loans	5	5
HELOCs | Updated FICO Score 620 Through 679
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	16	16
Revolving HELOCs amortized cost basis	6	6
HELOCs converted to term loans	10	10
HELOCs | Updated FICO Score 680 Through 739
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	74	87
Revolving HELOCs amortized cost basis	48	52
HELOCs converted to term loans	26	35
HELOCs | Updated FICO Score 740 And Above
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	382	487
Revolving HELOCs amortized cost basis	255	322
HELOCs converted to term loans	$ 127	$ 165